1. Field of the Invention
This invention relates to an automatic original feeding apparatus mounted on an image forming apparatus such as a printer or a copier.
2. Description of the Related Art
There are known image forming apparatuses such as printers and copiers having an automatic original feeding apparatus mounted thereon.
This automatic original feeding apparatus is openably and closably mounted on the upper surface of the main body of the image forming apparatus on which platen glass is disposed, and is designed to assume a closed position for covering the platen glass and an opened position in which it has been raised upwardly. The automatic original feeding apparatus has its closed position or opened position selected depending on whether an original used for image formation is a sheet-like one or a found one such as a book.
FIG. 9 of the accompanying drawings shows a hinge (rotary supporting mechanism) 50 for openably and closably supporting the main body of the automatic original feeding apparatus relative to the main body of the image forming apparatus. The hinge 50 comprises a cam 53 fixed to the main body 1 side of the image forming apparatus, and a hinge frame 51 fixed to the main body 2A side of the automatic original feeding apparatus, the cam 53 and the hinge frame 51 being rotatably connected together by a rotary shaft 52. The hinge 50 further comprises a spring (compression spring) 56 interposed between a housing 55 positioned on the hinge frame 51 through a slide shaft 61 and another housing 54 slidably supported by the hinge frame 51. The housing 54 is urged against the cam 53 by the spring 56 and conversely, the main body 2A of the automatic original feeding apparatus is biased counter-clockwisely about the rotary shaft 52 by the cam 53 through the spring 56. The rotational force of the main body 2A of the automatic original feeding apparatus about the rotary shaft 52 which is attributable to the gravity thereof is offset by this biasing. Therefore, the opening and closing operation of the main body 2A of the automatic original feeding apparatus becomes light. The spring 56 has its spring length gradually extended to decrease its biasing force by the housing 54 moving after the cam 53 as the main body 2A of the automatic original feeding apparatus is opened. This corresponds to the fact that the rotational force by the gravity becomes smaller as the opening angle of the main body 2A of the automatic original feeding apparatus becomes greater. That is, design is made such that at whatever position the main body 2A of the automatic original feeding apparatus may be opened, the rotational force by the gravity and the rotational force by the spring 56 are substantially offset by each other.
Also, Japanese Patent Application Laid-Open No. 54-50319 discloses an adjusting mechanism capable of adjusting the compressive force of a spring in accordance with the gravity of an original pressure plate provided on the upper portion of the main body of a copier and capable of being stopped at a predetermined angle for the hinge member of the original pressure plate.
However, according to the above-described automatic original feeding apparatus 2, for example, one used in a high-speed image forming apparatus great in the number of developed sheets per unit time is heavy and accordingly, as the spring 56 used in the hinge 51, use is made of one strong in spring force. Therefore, the unevenness of the spring force becomes great or the spring force is varied by long-period use. There has also been the problem that when the spring force strengthens, the closed position of the automatic original feeding apparatus deviates relative to the main body of the image forming apparatus and the automatic original feeding apparatus becomes incapable of being disposed at a regular position, and when conversely the spring force is too weak, the automatic original feeding apparatus will fall if it is released in its half-opened state.
Also, the compression spring adjusting mechanism disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 54-50319 has suffered from the problem that when a driver or the like is to be inserted into a groove formed in the rear end of an adjusting screw and be rotated to thereby adjust the compressive forced of the spring, a very great force is required and the working property of the adjusting work is bad. Also, a very great force is applied to the groove formed in the rear end of the adjusting screw, and this has led to the possibility of damaging the adjusting screw.
The present invention has been made in view of the above-noted circumstances and has as its object to provide an automatic original feeding apparatus of which the opening and closing relative to the main body of an image forming apparatus can be done well and in which the adjustment of a biasing force for assisting good opening and closing can be effected simply, and an image forming apparatus provided with the same.
The present invention for achieving the above object is an automatic original feeding apparatus mounted on the main body of an image forming apparatus for conveying an original to a predetermined position in the main body of the image forming apparatus, characterized by the provision of an automatic original feeding apparatus main body and rotary supporting means for openably and closably mounting the automatic original feeding apparatus main body relative to the main body of the image forming apparatus, the rotary supporting means including an opening and closing mechanism interposed between the main body of the image forming apparatus and the automatic original feeding apparatus main body and permitting the rotating operation of the automatic original feeding apparatus main body relative to the main body of the image forming apparatus, and a plurality of biasing members for biasing the automatic original feeding apparatus main body so as to offset the rotational force by the gravity thereof, at least one of the biasing members having an adjusting mechanism for adjusting the biasing force thereof.
Also, the present invention is the above-described automatic original feeding apparatus characterized in that the opening and closing mechanism has an immovable member fixed to the main body side of the image forming apparatus, a movable member fixed to the automatic original feeding apparatus main body side, and a rotary shaft for rotatably connecting the movable member to the immovable member.
Also, the present invention is the above-described automatic original feeding apparatus characterized in that the biasing members are interposed between the immovable member and the movable member.
Further, the present invention is an image forming apparatus provided with automatic original feeding means for conveying an original to a predetermined location in the main body of the image forming apparatus, reading means for reading the image information of the original conveyed to the predetermined location, and image forming means for forming an image on a sheet material on the basis of the image information read by the reading means, characterized in that the automatic original feeding means is the above-described automatic original feeding apparatus.